In infrared touch technology, the position of an object is measured based on determination as to whether infrared light is interfered with by the object.
An infrared signal used in the above method is an alternating current signal of several tens to several hundreds of KHz. Infrared signals are transmitted and alternating current signals collected depending on presence or absence of an object are averaged to measure magnitude of the signals.
In the above method, however, time to average the collected alternating current signals is necessary and frequency response of infrared touch measurement signal receiving units is considerably reduced due to high-frequency signals. As a result, sensitivity and overall response speed are lowered. Furthermore, different light sources operated in a light transmitting unit and a light receiving unit interfere with each other and, therefore, it is not possible for the light receiving unit to correctly receive signals. As a result, it is not possible to correctly calculate coordinates. In addition, in a case in which infrared signals are emitted between the light transmitting unit and the light receiving unit, a portion at which presence or absence of an object is not determined, i.e. ghost coordinates, may be generated at covered coordinates.
In order to solve the above problem, there has been proposed Korean Registered Patent No. 10-1018397 which discloses an apparatus and method for removing a ghost image. According to this disclosure, a first scan control mode is executed to remove a ghost image and, when multiple touches are sensed, a second scan control mode is additionally executed.
FIG. 14 is a view schematically showing construction of an infrared touch screen device that is capable of removing a ghost image disclosed in Korean Registered Patent No. 10-1018397.
According to the method disclosed in Korean Registered Patent No. 10-1018397, however, multiple touches may not be correctly recognized even when the multiple touches are actually generated in the first scan control mode.
Specifically, according to the method disclosed in Korean Registered Patent No. 10-1018397, in a case in which a new touch is generated, the first scan control mode is executed. In a case in which the touch is recognized as multiple touches, the second scan control mode is additionally executed to remove an object determined as a ghost image from the multiple touches. If the multiple touches frequently or rapidly move, even when subsequent multiple touches are generated during execution of the second scan control mode, it is not possible to perform switching to the first scan control mode with the result that it may not be possible to measure the subsequent multiple touches.